In European Patent EP-A-0,106,948 is described a process for obtaining magnets based on iron-cobalt-boron-rare earths alloy by the technique called powder metallurgy. While indeed the magnets obtained do have interesting magnetic properties, this process, on the other hand, proves to be particularly complicated and dangerous, in fact it requires numerous precautions to be taken, and especially working under a controlled atmosphere. Moreover, the cost of the magnets thus obtained is relatively high. Finally, while indeed the use of cobalt in the base mixture enables the Curie temperature to be increased quite significantly, and therefore the use temperature of these magnets, on the other hand, a reduction in the coercivity and magnetic properties in general are observed.
In the publication by SHIMODA et al. (J. Appl. Phys. 64 (10) 1988), it is proposed to produce permanent magnets based on a praseodymium-iron-boron-copper mixture and this is achieved with a low deformation ratio, especially less than ten. This production process is carried out by hot pressing under an inert atmosphere at approximately 1,000.degree. C. However, this process enables enhanced magnetic properties to be obtained for small magnets only. What i s more, taking into account their production process especially by sheath rolling, resulting indeed in a refinement of the grains (insufficient, however, with a deformation ratio less than ten), with an inhomogeneous microstructure and a magnetic orientation, only praseodymium enables good results to be obtained. It has been shown in fact that by replacing the praseodymium by neodymium, the magnetic properties fall off drastically, making the addition of copper totally pointless. Now praseodymium is much rarer in the earth's surface than neodymium, hence a cost of magnets based on praseodymium distinctly higher (typically in a ratio of 5 to 1 in relation to neodymium) .
There has also been described a hot welding process in European Patent EP-A-0,269,667 making it possible to obtain, under extensive safety conditions, permanent magnets on an industrial scale showing good magnetic performance. These magnets, based on iron-boron and rare earths have a relatively low production cost, taking into account the process used. Nevertheless, it is desirable to improve their magnetic properties. And this is the object of the present invention.